1. Field of the Invention
The present invention relates to a digital document management system or the like that manage document information including digital information and, more particularly, to a digital document management system, a digital document management method, and a digital document management program which are applied to digitization, distribution, storage of a document that needs weight of evidence as heavy as that a paper document provides and which are capable of easily identifying a corrected part in digital document information involving a partial correction (including, e.g., addition, change, deletion, sanitizing), guaranteeing the validity of the correction, and performing a third-party certification of the correction.
2. Description of the Related Art
As a prior art, a correction method and verification method of the validity of the correction used in a paper document will firstly be described.
Conventionally, as a representative correction method for use in performing correction for a paper document, there is known a method as shown in FIG. 69. That is, the method includes: crossing out characters to be corrected with a double line and entering proper characters in the space immediately above the correction (P1), putting signatures (initials) of both parties thereto (P2). Note that, in drawings, hereinafter, where the correction is made with a seal (name in a circle), this means the above correction method, that is, it corresponds to putting signatures of both parties thereto.
It is possible to guarantee/confirm the following points by conducting the above P1 and P2 in the conventional correction method for a paper document.
(1) Capable of easily confirming/identifying a corrected part, as well as capable of confirming that any other part than the corrected part includes no deliberate or negligent change.
(2) Capable of easily confirming/identifying corrected area.
(3) Capable of easily confirming a person who has made the correction.
(4) Capable of confirming whether the corrected part is a correctable part.
(5) Capable of confirming the original before correction.
(6) Capable of making a correction and verifying the correction according to a policy (control information) related to corrections.
Similarly, it is possible to guarantee/confirm the following points in the conventional correction method for a paper document with carbon-copied paper used for an insurance application form, transportation order form, or the like.
(7) Capable of partially hiding the document, as well as confirming that any other part than the hidden part includes no change.
(8) Capable of confirming the identity between a base paper and carbon-copied paper by comparing handwritings on respective papers.
(9) Capable of detecting falsification of document by separately storing the base paper and carbon-copied paper.
(10) Capable of performing a third-party certification related to the content of the document, even if being brought in court case, according to (9).
(11) The base paper and carbon-copied paper can be distributed as needed. In some cases, they can independently be distributed of each other.
As described above, a correction method and a method of certificating the validity of the correction in a paper document are excellent in various points. Meanwhile, along with recent advancement in IT technology, a technique that handles digital data (digital information) in place of the above paper document in view of convenience of data handling and data storage has been proposed (refer to, e.g., Jpn. Pat. Appln. Laid-Open Publications Nos. 2000-285024, 2001-117820, and 2003-114884, Paper of Information Processing Society of Japan/Computer Security Group (CSEC) “Digital document sanitizing problem (2003 Jul. 17) (2003-CSEC-22-009)”, and Paper of SCIS2004 “A Digital Document Sanitizing Scheme with Disclosure Condition Control”).
The above publications Nos. 2000-285024 and 2001-117820, which relate to a technique of storing the original of a digital document, propose techniques that give the properties that the original document (paper document) has to digital information and protect the digital document from being falsified. That is, these techniques focus that a mechanism for storing and managing a digital document of the final fixed version as an original document, that is, the storage location of the original document is made evident and focus how safely the original documents accumulated within an organization are stored.
However, in such an original document storage technique, even when only minor corrections are made for a digital document, it is regarded as “falsification”. For example, in the case of the abovementioned “corrections for paper agreement document”, a correction procedure of “crossing out word to be corrected with a double line, entering corrected word in the space immediately above the correction, and putting signatures of both parties”. In this case, even after corrections have been made for the paper agreement document, it is regarded as an original document.
The above correction procedure in a paper society is publicly judged to be valid and therefore the corrections made can be confirmed through a third-party certification.
On the other hand, in the case, even if the conventional original document storage technique, a problem that it is impossible to determine whether corrections are “falsification” or “proper change”. This can also be explained from the current feature of a digital signature which can detect every change made for a digital document.
The above publication No. 2003-114884, which relates to a digital document editing/displaying technique, proposes a technique for performing correction, addition and display control for a digital document on an element basis while guaranteeing the originality of the digital document without dividing the digital document into a plurality of parts. In this technique, original document information is constituted and managed by one file including actual data corresponding to original document information and a definition describing control for each element. When corrections or additions are made, they are described/added in/to the definition as correction information. As a result, a third-party certification related to the correction information can be achieved.
In this technique, however, it is necessary to reveal all correction information including previous versions in order to obtain a third-party certification. That is, a third-party certification cannot be achieved with a document a part of which is hidden (sanitized) or only with some versions.
The above paper “Digital document sanitizing problem” of CSEC, which relates to a digital document sanitizing technique, proposes a sanitizing technique applied to a digital document that solves a problem that a signature appended to a given document cannot be verified when a part of the document is made confidential. An application of the digital document sanitizing technique disclosed in the paper makes it possible to perform the signature verification even when sanitizing is applied to a digital document with a signature, to perform a third-party certification to certify that any other part than the sanitized part includes no change, and to perform “a third-party certification with a document a part of which is hidden (sanitized)” which has been pointed out as a problem of the publication no. 2003-114884.
In the digital document sanitizing technique of the paper, however, a creator of the original document is assured but it is impossible to identify who has performed the sanitizing. Further, the paper takes up the digital document sanitizing problem with a system of public offering of information as a usage scene of a digital document and has not mentioned about further utilization of the digital document under the condition that the document including some sanitized portions is distributed among a plurality of entities.